The present invention generally relates to liquid crystal display devices having lateral electrodes arranged in parallel to each other for receiving a scanning signal which addresses a scanning line along which an image is to be displayed and longitudinal electrodes arranged in parallel to each other for receiving a video signal corresponding to the image to be displayed along the scanning line, and in particular to a liquid crystal display device arranged such that each of the lateral electrodes are electrically connected to a signal bus carrying the scanning signal and each of the longitudinal electrodes are electrically connected to another signal bus carrying the video signal via respective switches which are addressed by a radiation beam and supply the scanning signal and the video signal selectively to the desired electrodes.
Liquid crystal display devices are widely used as an apparatus for displaying images. In such a case when using the liquid crystal display device to display a high definition image such as a television picture where a large number of picture elements are involved, a large number of lateral and longitudinal electrodes have to be used to achieve the required resolution. A conventional liquid crystal display device has lateral and longitudinal electrodes which are extended to the outer periphery of the liquid crystal display device for connection to lead wires. Each of the lateral electrodes are sequentially supplied with a scanning voltage signal which addresses a scanning line along which an image is displayed, and each of the longitudinal electrodes are supplied with a video signal corresponding to the image to be displayed along the scanning line addressed by the scanning signal. In the description hereinafter, such lateral electrodes will be referred to as "scanning electrodes", and such longitudinal electrodes will be referred to as "display electrodes".
Currently, it is difficult to manufacture a liquid crystal display panel having a large display area from a single liquid crystal display device, mainly because of the difficulty in achieving the required flatness and accuracy of parallelism of mutually facing substrates which are disposed in parallel to each other. Particularly, in the case of the liquid crystal display device using the so called active matrix driving system where a large number of driving circuit devices are formed on the substrate in a form of thin films so as to drive respective pixels, the size of the display device is particularly limited because of the limited yield of such circuit devices.
A liquid crystal display panel having a large display area is usually manufactured as an assembly of a large number of liquid crystal display devices. The liquid crystal display devices are assembled in a form of a matrix, and each of the scanning and display electrodes of a liquid crystal display device is connected to one of the corresponding scanning and display electrodes of adjacent liquid crystal display devices. In other words, the scanning and display electrodes of a liquid crystal display devices are connected to the corresponding scanning and display electrodes of adjacent liquid crystal display devices in one to one correspondence.
In such a liquid crystal display panel, a gap of at least two or three millimeters is required between the display devices in order to accommodate the wires connecting the liquid crystal display devices. As such a gap provides a passage of light from a light source provided behind the liquid crystal display panel, the gap is closed by an opaque mask so as to shut off the undesirable leakage of light. Such a gap closed by the opaque mask extends along the boundary between the liquid crystal display devices laterally and longitudinally and creates an undesirable region in which the image is not displayed. Such a gap appears quite conspicuous in the display area and gives an uncomfortable psychological feeling to the person watching the images on the display panel.
Although such a gap can be made not conspicuous by setting the distance between the electrodes to such a value comparable to the width of the gap and by applying an opaque coating to the region between the electrodes, the use of such a coating decreases the efficiency of utilization of the light radiated from the light source behind the liquid crystal display panel to below 40%, for example. In other words, the images displayed on the device becomes dark when such a coating is used.
In the conventional liquid display panel using the conventional liquid crystal display devices, a relatively large space or gap is inevitably required for accommodating the complicated wiring at the boundary of the liquid crystal display devices, and this gap cannot be satisfactorily reduced even with the use of extremely fine wires, or with the use of so called elastic connectors which connect the electrodes via an alternately stacked layers of conductors and non-conductors.
It should be noted that the number of the scanning and display electrodes used in the liquid crystal display panel having a large display area is enormous, and the entire scanning and display electrodes in the liquid crystal display panel are addressed at a same time. In other words, a series of video signals corresponding to an image to be displayed along a selected scanning line are supplied simultaneously to all of the display electrodes and the scanning signal addressing that scanning line is supplied to the corresponding scanning electrode extending throughout the liquid crystal display panel. Thus, the wiring connecting the individual electrodes to respective driving circuits also becomes complicated.
Further, there is a general tendency that the liquid crystal display device does not have a well defined threshold in the transmittance versus voltage characteristic curve. As a result, there is a tendency that a cross-talk appears between the neighboring pixels (See P.M. Alt and P. Pleshko, IEEE Trans.Electron Devices, ED-21 pp.146-155, 1977). In order to avoid such a cross-talk, one has to provide a sufficient separation between the neighboring electrodes. For this reason, the number of the electrodes addressed by the scanning signal in the line sequential addressing procedure is limited in the conventional liquid crystal display device. For example, the number of the scanning electrodes is limited to 64-130 for the cells using twist nematic liquid crystals and to 200-400 for the cells using super twist nematic liquid crystals (for example, see Wada, T. "Liquid crystal display devices using non-linear active devices" In: Liquid Crystals--Its Application--, K. Okano and S. Kobayashi (eds.) Chapter 4, pp.106-116, 1985 Baifukan, Tokyo). Thus, the construction of a large liquid crystal display panel using a large number of electrodes exceeding these numbers is extremely difficult as long as the conventional liquid crystal display devices are used.
Moreover, the frame frequency for addressing the scanning line is usually set to 16-64 Hz. Thus, the duration in which a particular scanning line is addressed decreases with an increase in the number of scanning lines. On the other hand, the liquid crystal usually requires several tens of milliseconds in order to respond. Thus, when the number of scanning lines is large, the time interval required for addressing the numerous scanning lines becomes excessive due to the accumulation of the response times. The effect of such a limited response time of the liquid crystal display device becomes particularly conspicuous when a motion picture is displayed. In such a case, the liquid crystal cannot follow the change in the picture and the contrast of the displayed picture is deteriorated.